This invention relates to an apparatus for delivering a succession of sheets from a sheet cutting device which cross cuts a web into sheets, the web being of paper, foil, fabric, metal, synthetics or similar materials. The sheets are delivered to a sheet collecting cylinder at which stacks of sheets are temporarily collected and formed into a stack which is then deposited to a sheet stack depository station at a rate of travel less than the rate of delivery of sheets to the collecting cylinder. Delivery is effected by opposing conveyor tapes.
German published patent application DE-OS No. 14 61 211 discloses an apparatus of this general type in which sheets formed by cross cutting a web are delivered toward a sheet collecting cylinder as the sheets pass between a pair of conveyors moving at a fast rate of speed. The sheet collecting cylinder collects a plurality of sheets to form a sheet stack. Another pair of opposing conveyors downstream of the collecting cylinder is provided for delivering the stack moving between them to a stack depository. Such another pair of conveyors initially move at a rate of speed equal to the rate of travel of the conveyors upstream of the collecting cylinder when taking over the stack. Thereafter the downstream conveyors are decelerated to about 1/10th of their former speed. Once the stack is deposited, the downstream conveyors are accelerated in order to take over another stack of sheets. Therefore, not only the downstream conveyors but their guide rollers as well must be decelerated and accelerated. Because of the mass of the rollers inertia forces arise when decelerating and accelerating. Moreover, the downstream conveyors are designed to slip during acceleration and deceleration relative to their guide rollers. These inertia forces which develop are unwieldy requiring additional power and power control. And, the sheet stacks are difficult to control when being delivered to the depository.
German patent DE-AS No. 10 31 322 discloses another related apparatus in which the sheet stacks to be deposited are decelerated in such a manner that the trailing end of each stack is gripped by clamping jaws located between opposed conveyor tapes which move at a relatively high speed. The gripped stack is accordingly slowed down such that the speed of the stack to be deposited is abruptly changed. The individual sheets of the stack can therefore shift relative to one another making it difficult to properly deposit all the sheets of the stack. Also, gripping by the clamping jaws can effect undesirable marks on the sheets. And, the opposed conveyor tapes located downstream of the collecting cylinder are disposed within a pair of hinged covers which must open against the force of a spring whenever the sheet stack moves at the reduced speed. This creates inertia forces of undesirable magnitude and limits the operating speed of the apparatus.
British Pat. No. 857,871 discloses yet another related apparatus in which sheet stacks overlap one another as they are successively fed on top of preceeding sheets. A sheet stack is delivered by slowly rotating rollers intermediate opposing pairs of conveyor tapes for decelerating the stacks when delivered to the depository. Since deceleration is effected by these rollers, undesired markings on the sheets to be deposited easily occur. Moreover, the sheets of a sheet stack can easily slide relative to one another, which is undesirable. And, the individual sheet stacks slide relative to each other when they reach the depository, such that the deposit of a squared-off stack is not assured.